Antenna measurements with RF noise source

Using the wide band characteristics of SDR radios, it is possible replicate some of the functionality of much more expensive equipment such as a vector network analyzer.  Actually what SDR can do it scalar network analyzer functionality. A scalar network analyzer can measure amplitude, but a vector network analyzer can measure amplitude and phase and is a more complex device. I have already measured RF filters with my RF noise source and RTL-SDR. Next step is antenna measurements.

SWR stands for “standing wave ratio” and is a measure that can be used to tune an antenna for a particular frequency. The closer the SWR is to 1:1 at the designed antenna frequency, the better the antenna will receive (and transmit).

RTL-SDR Tutorial: Measuring filter characteristics and antenna VSWR with an RTL-SDR and noise source article tells that in addition to SDR and noise source  for determining VSWR you will also need a directional coupler. To measure the VSWR of an antenna we will use the directional coupler in reverse: connect the noise source to the output of the coupler, the antenna to the input of the coupler and the RTL-SDR dongle to the coupling (CPL) port of the coupler.

Suitable software to view results are for example  Spektrum RTL-SDR Spectrum Analyzer Software and  GUI for rtl_power.

Here are some instructional videos how to make measurements:

DIY Characterize the antenna Retrurn Loss / SWR with the DVB-T SDR

#158: Directional Coupler Basics & how to sweep SWR of an antenna | Return Loss | VSWR

How to measure return loss of a 978 MHz antenna

This is the end of this post. I am still in the process of trying to find the optimum way to measure the antennas with RTL-SDR.

At the moment I don’t have a good 50 ohms directional coupler for doing the measurements. I am experimenting with some ideas with the hardware I already have to see if I could live without investing to a possibly expensive and hard to get directional coupler. I plan to write results of those experiments later when I get more results.


Documents that tell how to do antenna measurements:

RTL-SDR Tutorial: Measuring filter characteristics and antenna VSWR with an RTL-SDR and noise source

SDR Based Antenna and Filter Analyzer

Antenna tuning

Noise generator and rtl_power for antenna testing. (self.RTLSDR)

Characterizing the SWR of an Antenna with a Noise Source and an RTL-SDR

Using the Airspy as a Network Analyzer for Characterizing Antennas

Measuring Filters and VSWR With RTL-SDR


  1. Tomi Engdahl says:

    Antenna Basics by Whiteboard

    [Bruce] did a video about antenna basics where he spends a little more than a half hour discussing antennas.

    How do antennas work?


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